1. Preheat the oven to 350 degrees Fahrenheit. Press 1 pie crusts into a pie pan, flute the edges, poke holes in the bottom and pre-bake for about 10 minutes.
2. Melt the margarine in a medium saucepan, over medium heat. Add the onions, celery and carrots and cook until the onions are soft, about 10 minutes. Add the peas, corn and seitan, stir and remove from the heat.
3. As the vegetables are cooking, prepare the gravy as directed on the package, and add the rosemary. When the gravy is done, pour it over the vegetables and seitan.
4. Pour this mixture into the pie crust. Place the other pie crust atop the pie, cut off any crust that hangs over the edge and press the edge into the edge of the bottom crust.
5. Cut vents in the top crust and bake for 30 minutes, or until the top crust is browned (or until the gravy starts to bubble up).